1. Field of the Invention
The present invention relates to flat flexible electrical jumpers comprising a plurality of flat connectors contained within an insulation material. More specifically, the invention relates to an improved method of manufacture to enable several flat flexible jumper configurations to be manufactured without requiring changes in the tooling.
2. Description of the Related Art
In the past, most flexible jumpers comprised strands of round wires housed in a rounded shell of insulation. Once the desirability for flat flexible jumpers increased in the art, several companies developed various designs and manufacturing methods for producing a flat flexible cable. Generally, flat flexible cables of the prior art comprise a connection portion on each end of the cable shaped to mate with their respective mating connector and a flat conduction portion linking each end of the connector.
U.S. Pat. No. 3,601,755, issued to Shiells, etal. and assigned to Thomas and Betts, discloses a flexible flat jumper strip. The jumper strip is formed by aligning a series of round wires in a row and rolling down a central portion of each wire to form the thin flat cross section of the conduction portion. This process results in a jumper with two identically sized and shaped round connection portions on each end of the jumper and a flat central conduction portion. Since the rolling of the round wires creates the flat conduction portion, the dimensions of the flat conduction zone result from the cross-sectional area of the round zone.
For example, creating a jumper using the above method with a connection portion having a 0.02 inch diameter and a flat conduction portion of 0.004 inches thick would result in the following other parameters. Since the desired jumper has a round connection portion of a 0.020 inch diameter, the cross-sectional area of the connection portion by definition is 0.000314 square inches. Following the above procedure, the central portion of the wire is rolled down to a rectangular cross-section with a 0.004 inch thickness. After rolling, the wire will necessarily have an approximate width of 0.080 to maintain the original 0.000314 square inch cross-sectional area of the round connection portion. If each wire in the flat conduction portion touched each other, then the minimum distance between the center of each flat wire conductor would be 0.08 inches. Since it is not desirable to let the wires touch each other, a thin layer of insulation is placed between each wire. The minimum distance between the center point of each round connection end of the wire must necessarily be equivalent to the minimum spacing between the flat section of each wire. In the above example, even without the placement of insulation between each wire, the distance between each round connection end of the jumper wires, also referred to as the pitch, is at least 0.08 inches apart. Therefore, the minimum pitch of a connector with a round wire of 0.02 inches in diameter and a 0.004 inch thickness in the central portion is 0.08 inches. Using the above method, it would be impossible to produce a conductor with wires spaced at a pitch of 0.050 inches, having a round zone of 0.02 inches in diameter and a thickness of 0.004 inches. Therefore, as illustrated by the above example, it is undesirable to have the cross sectional area of the round connection portion, i.e., the diameter of the round zone, directly related to the cross sectional area of the flat zone as it limits the numbers of possible jumper configurations.
In addition, the rolling process is often inconsistently applied depending on where and if the roller contacts each wire. The inconsistent application of the coining or rolling operation causes slight variations in the thickness of the flat zone. Variations in the thickness of the flat zone cause variations in the flexibility life of the jumper. Inconsistencies in the flexibility and life of the jumper are undesirable, as they can cause premature and unexpected failure to result in the jumper.
Further, the coining operation changes the original mechanical properties of the wire, such as tensile strength, hardness, elongation and flexibility. If a preplated wire is used in a jumper that is formed by rolling, the preplated wire will be work-hardened and cannot be annealed. This alteration of the mechanical properties of the wire is undesirable, since a work-hardened metal is more susceptible to fatigue. Therefore, there exists a need in the art for an improved manufacturing process to produce flexible jumpers without altering the mechanical properties of the wires which form the jumpers.
Another method of the prior art, utilizes a flat strip of conductive material of a given thickness which is stamped at various locations to form sections of thinner widths. Using this method, if it is desirable to obtain a cross-sectional area that is thinner than the original thickness, the strips of metal are coined down, and the material in excess of the desired width is removed.
For example, if the thickness of the strip is 0.020 inches, the maximum thickness of the connection zone is 0.020 inches thick. If a flat zone is 0.010 inches thick, the flat zone is coined down to approximately 0.010 inches and results in a 0.040 inch width, thus the desired reduced thickness of 0.010 inches is achieved. However, if the flat zone having a width of 0.040 inches is too large, a cutting die is used to remove the material in excess of the desired strip width. If an even thinner flat zone is desired, another coining operation can be used to reduce the thickness to 0.004 inches. This coining operation will necessarily increase the width to 0.060 inches. If a reduced width is desired, a cutting die will be used to remove any material in excess of the desired pitch.
This method requires a number of individually sized dies to cut back the material to the desired strip width. Additionally, an additional die is required to cut each length of the connector. The increased tooling costs that are required to manufacture each of the individual dies make this manufacturing method very costly.
Further, the multiple coining and cutting steps workharden the material with each process that is performed on the wire. Therefore, the undesired alteration of the mechanical properties of the metal is more severe in this method of manufacturing than in the previous method.
Finally, U.S. Pat. No. 4,107,836, issued to Roberts and assigned to Advanced Circuit Technology discloses a flexible flat jumper strip which is made by chemical etching. In order to form a jumper by the chemical etching process, a strip of conductive metal of a thickness equivalent to the largest thickness that is desired for the jumper is formed. A masking pattern is laid over the length of the jumper material, and those portions which are to remain at the current thickness of the material are indicated on the pattern. The pattern of the blocked off areas is formed on an etching mask by a conventional photolithography process. A traditional chemical etching procedure is then performed using the etching masks to remove the material in those areas which are not blocked off by the chemical etching mask thereby achieving the desired width in these areas.
This process enables custom jumpers to be made as easily as standard jumpers. However, a separate etching mask must be made for each configuration, and the costs associated with making an etching mask are extremely high. Further, there are several factors in the chemical masking process that limit the amount of material that can be etched off in a single procedure. Therefore, there is a limit to the thickness variation between the central flat portion and the connection portion. The main disadvantage of this jumper manufacturing method is its high costs.
Therefore, there exists a need in the prior art for a thin, flexible jumper cable that can be manufactured in several different configurations without requiring the high tooling costs associated with the prior art jumper manufacturing methods and without changing the mechanical properties of the metal which forms the jumper.